The present invention relates generally to the field of automatic transmission systems and, more particularly, to an improved forward clutch control valve assembly for use in Ford AX4N transmissions and other similar transmissions.
Automatic transmission systems of the prior art have a hydraulic circuit subsystem which includes at least a hydraulic pump, a valve body having fluid conducting passages or circuits, input and exhaust ports formed within the fluid circuits, and a plurality of spool valves so-called because of their resemblance to sewing-thread type spools. Such valves are comprised of generally cylindrical pistons having control diameters or lands formed thereon, which alternately open and close the ports to the fluid circuits to regulate the flow and pressure of automatic transmission fluid (hereinafter xe2x80x9cATFxe2x80x9d) in order to charge the fluid circuits and actuate the hydraulic components of the transmission. It will be understood that in describing hydraulic circuits, ATF usually changes names when it passes through an orifice or control valve in a specific fluid circuit.
In the Ford AX4N automatic translate (hereinafter xe2x80x9cFord translatexe2x80x9d), the forward clutch control valve regulates the flow of ATF from the pump to operate the forward clutch via the 1-2 shift valve circuit and the 3-4 shift valve circuit. The original equipment manufacture (hereinafter xe2x80x9cOEMxe2x80x9d) forward clutch control valve is an aluminum spool valve, which is configured with a pair of control lands interconnected by a valve stem and terminates in a narrow front valve stem whereon a compression spring resides. During operation the front valve stem typically strikes against a steel retaining clip that secures the valve within the valve body when the forward control valve is stroked. This striking action between the front valve stem and retaining clip causes the OEM valve to bend and eventually the valve can become seized in the bore causing a malfunction of the forward clutch.
Thus, the present invention has been developed to resolve this problem and other shortcomings of the prior art.
Accordingly, the present invention is a forward clutch control valve assembly for the Ford AX4N translate and similar transaxles including a primary control land having an increased outside diameter and axial length, which replaces the narrow forward stem of the OEM valve piston. The increased axial length of the primary control land on the present valve piston is based on the limits of axial travel of the piston within the cylindrical bore wherein the valve piston resides during operation.
The present forward clutch control valve assembly provides a substantially increased control land-to-bore surface contact ratio and also provides an increased end face surface area for contact with the aforementioned steel retaining clip. As a result the present forward clutch control valve assembly is substantially less prone to bending and/or seizure within its mating bore during operation.
The present forward clutch control valve assembly is provided in kit form including a replacement compression spring, which is substituted for the OEM spring when the present forward clutch control valve assembly is installed. A bore-sizing tool is also provided to resize the mating bore in the valve body to retrofit the present valve to the Ford AX4N translate.
Other features and technical advantages of the present invention will become apparent from a study of the following description and the accompanying drawings.